The invention relates to the use of ion-complexing resin beds in water purification systems, and more particularly, to a resin trap device for removing resin particles in ultrafiltration systems.
The production of ultrapure water is essential to the fabrication of defect-free silicon chips in the microelectronics industry. Typically, producing ultrapure water involves treating water through a number of processes to remove ion contaminants. In particular, the ultrapure water (also known as deionized or high filtered water) must be virtually free of ionic contaminants, typically bringing the specific resistivity to greater than or equal to about 18.2 Mxc2x7ohmxc2x7cm at 20xc2x0 C.
In these water purification systems, water is initially treated by a series of steps which control the pH level of the intake water, add chlorine to control bacteria growth in the water, remove particulate matter, remove added chlorine so that it does not damage delicate downstream equipment, and warm the water to about 21xc2x0 C. (20xc2x0 F.). After these initial treatment steps, the water is typically deionized in a reverse osmosis process and then degassed. The water is then further deionized by a first set of resin beds. The resin beds include beads of an ion-complexing resin which are retained in the resin beds by a screen on the exit header pipes and laterals inside the bed. The water passes through the resin beds so that it intimately contacts the resin beads to remove ion contaminants from the water. The water then passes through a plurality of 1.0 xcexcm particle pass size microfiltration modules or microfilters to remove resin particles which may have escaped the resin beds and entered the water purification system. These microfilters contain membranes of spun polypropylene or nylon which are housed in a stainless steel housing and arranged so that water enters the outer lumens of each microfilter and permeates to a common inner plenum within the housing. The water passes through the microfilters to an ultraviolet sterilization unit to control bacterial contamination and is typically stored as deionized water.
The deionized water from storage is then treated by a second set of water purification steps. These water purification steps include ultraviolet sterilization to control bacterial contamination and to convert organic materials to low molecular weight charged ions, and polishing reverse osmosis for the removal of charged ions and particulate matter. The water then passes through a final polishing system which includes another ultraviolet sterilizer and a second set of ion-complexing resin beds to remove ion contaminants from the water. Another set of microfilters is positioned downstream from the second set of resin beds to remove resin particles which may escape from the resin beds. These microfilters also have a small particle pass size (e.g. 1 xcexcm absolute and 0.1 xcexcm or 0.2 xcexcm nominal rated) and include a polyvinylidene fluoride (PVDF) lined stainless steel housing to avoid parts per trillion metals contamination. Immediately after passing through these microfilters, the water advances to a set of cross-flow ultrafilters that remove additional ion contaminants and very small particles to produce ultrapure water.
One problem that occurs in these water purification processes is that resin particles escape the ion-complexing beds and become entrained in the water flow. This xe2x80x9cfoulingxe2x80x9d of the water occurs, to some degree, during normal system operation of the purification system. However, events such as the breakage of exit flow strainers in the resin beds can cause a sudden large release of resin particles into the flow of water. This sudden release of resin particles can blind downstream microfilters and ultrafilters and clog system apertures and instrumentation thereby reducing or stopping the flow of water in the ultrafiltration process.
As mentioned above, the conventional method of removing resin particles from the water purification system prior to ultrafiltration is to use a plurality of microfilters having a maximum particle pass size of between 0.1 and 1 xcexcm. Unfortunately, because of the small particle pass size of these microfilters, the high pressure drop through these microfilters significantly decreases the flow rate of the water through the water purification system. Therefore, ultrapure water often cannot be produced at the flow rates desired for manufacturing processes.
An additional problem associated with these microfilters is that it can be difficult to remove the resin particles trapped in the microfilters. In particular, these microfilters cannot be flushed and thus resin particles accumulate in the microfilters. As a result, this accumulation makes it necessary to replace the microfilters in the water purification system on an annual or biannual basis. In particular, if these microfilters are not replaced, the water can become more readily contaminated and resin particles are more likely to be released into the water purification system. The replacement of microfilters causes great expense to the operation of the water purification system not only because the microfilters are expensive but because their replacement also requires that the entire purification system be shut down and opened to the atmosphere.
There is therefore a need in the art of ultrapure water systems for an apparatus and method to remove potentially damaging resin particles from the flow of water that does not cause an undesirable pressure drop, is not subject to contamination and is suitable for continuous operation and cleansing by flushing with water.
The present invention is a resin trap device and method of using same to remove large resin particles from the water in a water purification system. In particular, the resin trap device removes large resin particles to protect downstream ultrafiltration equipment from damage even when large releases of resin particles enter the purification system such as by breakage of the resin bed exit flow strainer in the system. The resin trap device of the invention does not cause an undesirable pressure drop in the water flow thereby allowing ultrapure water to be produced at good flow rates. In addition, the resin trap device can be cleansed by flushing with water or disassembly to remove resin particles and thus limit contamination of the water and the need to replace filtration apparatus on an annual or biannual basis.
In accordance with the present invention, it has been discovered that it is not necessary to remove resin particles down to micron size prior to the ultrafiltration of water. In particular, it has been discovered that a light flow of small particles having an average diameter of less than about 150 xcexcm (6 mils) generally does not harm the ultrafiltration equipment and these small particles can be harmlessly diverted into a reject water stream and tapped out of the ultrafiltration system. Large resin particles having an average diameter of greater than about 150 xcexcm, on the other hand, can harm the cross-flow ultrafiltration membranes found in the final cross-flow ultrafilters and can also harm other delicate equipment located downstream from the resin beds. Therefore, it has been determined that damage to the ultrafilters can be avoided by removing the large resin particles from the water purification system.
The present invention comprises a resin trap device for removing large resin particles from a water purification system. The resin trap device comprises a housing and one or more resin strainers disposed within the housing. Each resin strainer includes a plurality of openings having a particle pass size of between about 100 xcexcm (4 mils) and about 250 xcexcm (10 mils) thereby allowing water and particles having a particle size of less than the particle pass size to flow through the openings but not allowing particles having a particle size of greater than the particle pass size to flow through the openings. Preferably, the particle pass size is between about 125 xcexcm (5 mils) and about 175 xcexcm (7 mils), and more preferably, about 150 xcexcm. By using resin strainers having these particle pass sizes, the majority, if not all, of the large resin particles can be removed while still maintaining a minimal pressure drop across the resin trap device. As a result, ultrapure water can be produced at good flow rates and delivered at these rates to specific end uses.
The resin trap device of the invention can be included in a water purification system which comprises a source of water, a resin bed, and the resin trap device. The resin bed comprises an inlet for receiving water from the water source, a plurality of resin particles for intimately contacting the water and removing ions from the water, and an outlet. The resin trap device is external to the resin bed and in fluid communication with the outlet of the resin bed. In accordance with the invention, water and any particles entrained therein flow from the resin beds into the resin trap device and large particles having a diameter of greater than the particle pass size of the openings are retained in the resin trap device to prevent damage to downstream ultrafiltration equipment. Water and small particles having a diameter of less than the particle pass size of the openings flow through the openings, exit the resin trap device, and further advance to the ultrafiltration system. The small particles that enter the ultrafilters in the ultrafiltration system can then be easily diverted into a reject water stream and removed from the ultrafiltration system. The resulting filtrate from the ultrafiltration system is suitable for ultrapure water applications.
The present invention also includes a method of purifying and filtering water to produce water suitable for ultrafiltration. First, water is passed through a resin bed and intimately contacted with resin particles to remove ions from the water and thereby purify the water. The purified water that exits the resin bed is then advanced from the resin bed into a resin trap device comprising a housing and a resin strainer disposed within the housing. The resin strainer contains a plurality of openings having a predetermined particle pass size as described above and retains large particles having a diameter of greater than the particle pass size and allows water and small particles having a diameter of less than the particle pass size to flow through the resin trap device.
In one preferred embodiment of the invention, water is advanced from the resin bed directly into the housing, large particles are retained in the housing, and water and small particles are allowed to flow from the housing into the resin strainer and out of the resin trap device. In this embodiment, a fluid inlet in said housing is in fluid communication with the outlet of the resin bed and the resin strainer comprises an outlet. The water from the outlet of the resin bed enters through the fluid inlet in the housing, water and small particles pass through the openings in the resin strainer to an outlet of the resin strainer, the water and small particles exit the resin trap device through an outlet in the resin strainer, and the large particles are retained in the housing by the resin strainer.
In another preferred embodiment of the invention, water is advanced from the resin bed directly into the resin strainer, large particles are retained in the resin strainer, and water and small particles are allowed to flow from the resin strainer into the housing and out of the resin trap device. In this embodiment, the resin strainer further comprises an inlet in fluid communication with the outlet of the resin bed. The water from the outlet of the resin bed enters through the inlet of the resin strainer, the water and small particles pass through the openings into the housing, the water and small particles exit the housing through the outlet in the housing, and large particles are retained in the resin strainer.
In yet another preferred embodiment of the invention, the resin trap device comprises a housing including a fluid inlet for receiving a flow of water, a plurality of spherical resin strainers disposed within the housing, and a primary outlet in fluid communication with each of the resin strainers to allow the flow of water out of the resin trap device. The resin strainers each include a plurality of openings having a predetermined particle pass size as described above so that water enters the resin trap device through the inlet of the housing, water and small particles having a diameter of less than the particle pass size flow from the housing into the resin strainers through the openings and out of the resin trap device through the primary outlet, and large particles having a diameter of greater than the particle pass size are retained in the housing. The resin trap device can further include a plurality of secondary fluid outlets, each of which corresponds to a resin strainer and is in fluid communication with the primary outlet so that water and small particles flow from the resin strainers through the secondary outlets into the primary outlet and out of the resin trap device.
The resin trap device can be easily cleaned by flushing water through the resin trap device to force particles retained in the resin trap device into an auxiliary drain line. Typically, a valve attached to an outlet of the housing or the resin strainer is manipulated to provide water to clean the resin trap device. Alternatively, the resin trap device can be cleaned by isolation, removal and disassembly of the resin trap device. In either case, multiple resin trap devices are preferably provided in a parallel flow configuration to ensure continuous operation even during cleaning of one or more of the resin trap devices.
These and other features and advantages of the present invention will become more readily apparent to those skilled in the art upon consideration of the following detailed description and accompanying drawings which describe both the preferred and alternative embodiments of the present invention.